A228872 Odd numbers producing 3 decreasing odd numbers in the Collatz (3x+1) iteration.

13, 53, 113, 213, 453, 853, 909, 1813, 3413, 3637, 7253, 7281, 13653, 14549, 29013, 29125, 54613, 58197, 58253, 116053, 116501, 218453, 232789, 233013, 464213, 466005, 466033, 873813, 931157, 932053, 1856853, 1864021, 1864133, 3495253, 3724629, 3728213

Offset

1,1

Comments

Sequence A198584 gives the first term of the Collatz sequence having exactly 3 odd numbers. This sequence is the subset of A198584 for which the second odd number is smaller than the first.

Links

Table of n, a(n) for n=1..36.

Example

The number 13 has the Collatz iteration {13, 40, 20, 10, 5, 16, 8, 4, 2, 1}, which has three odd numbers in decreasing order {13, 5, 1}.

Mathematica

donQ[n_]:=Module[{od=Differences[Select[NestWhileList[If[EvenQ[#], #/2, 3#+1]&, n, #>1&], OddQ]]}, Length[ od] ==2&&Max[od]<0]; Select[Range[1, 373*10^4, 2], donQ] (* Harvey P. Dale, Sep 23 2019 *)

Crossrefs

Cf. A198584 (Collatz iterations having 3 odd numbers).

Cf. A228871 (Collatz iterations producing 3 out-of-order odd numbers).

Sequence in context: A031905 A214523 A087880 * A041322 A022284 A179549

Adjacent sequences: A228869 A228870 A228871 * A228873 A228874 A228875

Keyword

nonn

Author

T. D. Noe, Sep 12 2013

Status

approved